1. Field of the Invention
Aspects of the present invention relate to an electrolyte membrane for a fuel cell and a fuel cell using the same.
2. Description of the Related Art
Fuel cells, which use a polymer electrolyte membrane as an electrolyte, operate at a relatively low temperature and can be small in size. Thus, such fuel cells are expected to be used as energy sources in electric vehicles or distributed generation systems in homes. As a polymer electrolyte membrane used in polymer electrolyte fuel cells, a perfluorocarbon sulfonic acid-based polymer membrane available as NAFION® available from E.I. du Pont de Nemours and Company is used.
However, such polymer electrolyte membranes require water in order to sufficiently conduct protons, and thus the polymer electrolyte membranes require humidification. In addition, to enhance cell system efficiencies, it is necessary to operate polymer electrolyte membranes at a high temperature, i.e., at least 100° C. However, the moisture in the polymer electrolyte membrane is evaporated at such temperatures, and polymer electrolyte membranes cannot function as a solid electrolyte.
To address such problems in the related art, non-humidified electrolyte membranes, which can operate at a high temperature of at least 100° C. without humidification, have been developed. For example, Japanese Patent Laid-Open Publication No. 11-503262 discloses a polybenzimidazole doped with a phosphoric acid, and the like, as a material for use as a non-humidified electrolyte membrane.
In addition, in cells which operate at a low temperature, such as the cells using a perfluorocarbon sulfonic acid-based polymer membrane, electrodes using polytetrafluoroethylene (PTFE) as a waterproof agent having hydrophobic properties have been widely used to prevent gas diffusion in the electrodes due to formation of water produced as electricity is generated in an electrode, particularly a cathode. For example, Japanese Patent Laid-Open Publication No. 05-283082 discloses use of such electrodes.
In addition, phosphoric acid fuel cells operating at a high temperature, i.e., 150 to 200° C., use a liquid phosphoric acid as an electrolyte. However, a large amount of the liquid phosphoric acid therein interferes with gas diffusion in the electrodes. Therefore, an electrode catalyst layer including a polytetrafluoroethylene (PTFE) as a waterproof agent, which prevents fine pores in the electrodes from being clogged by the phosphoric acid, has been used.
In addition, in fuel cells using a polybenzimidazole (PBI) electrolyte membrane, which uses a phosphoric acid as a nonhumidified electrolyte at a high temperature to reduce contact between electrodes and the electrolyte membrane, a method of impregnating the electrodes with a liquid phosphoric acid has been used and a method of increasing a loading amount of metal catalysts has been used. However, such fuel cells do not exhibit improved properties. In addition, the electrolyte membrane formed of PBI does not have satisfactory mechanical properties, chemical stability, or the capability of containing a phosphoric acid. Thus, there is still a need for improvement.